code: def _validate_vastai_creds(self, api_key: str):
      client = api_client.VastAIAPIClient(api_key=api_key)
      if not client.auth_test():
          raise_invalid_credentials_error(fields=[["creds", "api_key"]])
  
file_path: dstack/src/dstack/_internal/server/services/backends/configurators/vastai.py
imports: import json
  from typing import List
  from dstack._internal.core.backends.vastai import VastAIBackend, api_client
  from dstack._internal.core.backends.vastai.config import VastAIConfig
  from dstack._internal.core.models.backends.base import BackendType, ConfigElementValue, ConfigMultiElement
  from dstack._internal.core.models.backends.vastai import AnyVastAIConfigInfo, VastAIConfigInfo, VastAIConfigInfoWithCreds, VastAIConfigInfoWithCredsPartial, VastAIConfigValues, VastAICreds, VastAIStoredConfig
  from dstack._internal.server.models import BackendModel, ProjectModel
  from dstack._internal.server.services.backends.configurators.base import Configurator, raise_invalid_credentials_error
label_desc: Use image node_id 7 for calling the VastAIConfigurator obj's underlying member method code with example usage: obj._validate_vastai_creds(api_key) without return types